1. Field of the Invention
The present invention relates to an image data processor for generating a page raster that is image data rasterized by each page based on page description data described in page description language for variable printing and an image data processing program storage medium storing an image data processing program that causes an information processing apparatus to operate as the image data processor.
2. Description of the Related Art
For example, there have been variable printing in which a variable object that is an image object used only once on a particular page is combined with a reusable object that is an image object used repeatedly over plural pages. One application of the variable printing is, for example, an advertisement addressed to a different individual name but contents of which is almost the same, for example, formed by picture patterns.
As variable printing has large data volume due to its abundant variation in printing, how to decrease data amount, speed up processing and suppress the amount of data storage capacity is a problem.
Here, there has been proposed a technique for decreasing the storage raster amount by paying attention to correlation between pages in variable printing (see Japanese Patent Application Publication No. 2005-167537).
Japanese Patent Application Publication No. 2005-167537 has proposed the following feature to solve the above problem.
Generally in variable printing, reusable objects are arranged on the most areas of a page, and a variable object is arranged on a small area of the page. Thus, each page has a similar construction Here, similar pages are extracted to form one group. Image for one page in the group is referred to as a reference image. Pixel difference between other pages in the group and the reference image is calculated. The most regions of the differential image are white pixels and thus compressed effectively with a high compression ratio. This can reduce total storage capacity.
However, the feature of this technique lies in that, at the time of data production, differential operation for two images is performed over the entire page and compression operation for differential image having the page size is performed. In addition, at the time of using the data (at printing), expansion operation is performed for the differential image having the page size. Subsequently, addition operation similar to differential operation is performed for two images over the entire page. As these operations require high load processing, Japanese Patent Application Publication No. 2005-1675 has provided an exclusive hardware for these operations.
It may be said that the technique disclosed in Japanese Patent Application Publication No. 2005-167537 is slow processing and requires high cost for speeding up processing.